Hard surface material including slate, stone, ceramic tiles, marble, etc. has to be installed over a rigid surface that will not flex or "give". The rigid material is used to cover a floor or wall, and will accept the ceramic or hard surface materials and the mortar or cements used to attach them. This is true whether the construction is a new housing project or when renovating the floors or walls of an existing home or commercial structure.
Most residential homes are built on either a concrete slab or a wood frame sub-floor. The two types of surfaces are quire different. Each has special characteristics of material that will affect the type of flooring that is installed.
The subject of the present invention relates to a flooring and all similar types of hard surface flooring or wall tiles.
The material usually referred to as the floor is really the "skin" over the real floor of a structure. The real floor is a structural floor that holds up walls, furnishings of the house and occupants of the house. The floor also serves to keep out moisture and the elements of nature.
Floors that are to be covered with ceramic tiles, stone or other hard surface materials must be specifically constructed to accept these materials. Concrete slab floors are strong and durable and provide an excellent bonding for hard surface floor skins such as tile, stone, or marble. A concrete floor that is properly prepared will accept almost any type of hard surface flooring. While concrete is not waterproof, and retains a certain amount of moisture after it has been poured, it is easily adaptable for the installation of all hard surface flooring materials.
When installing ceramic tile on a concrete slab, a mortar bed typically is used. This is a procedure requiring great skill, and some mortar installations are older than written history. When installing hard surface materials over a concrete slab weight is not an issue. When installing ceramic or stone tile over a concrete slab floor, a mortar base is applied to the floor and the tiles are set level in the mortar. Grout is then applied in the spaces between the tile or stone.
The beauty and lasting durability and color of ceramic or stone tile make it a very desirable floor covering. Installing tile or stone on a concrete floor is relatively straight forward. A skilled craftsman applies a mortar base of cement over a screen that is designed to hold the mortar. More than one layer of mortar is usually necessary which means that time for the first layer to dry is necessary. A second layer of mortar is laid and the ceramic or stone tiles are installed in a grid like pattern.
U.S. Pat. No. 5,052,161 is of interest, as the patent explains in detail the old "mud setting bed" composed of at lean mixture of sand and cement. The patent describes how modern tile setting avoids direct bonding to concrete or wood substrates as such a system causes problems with cracking, especially on a cement subfloor or base. The patent calls for a thin plastic film containing bubbles to be placed between the base of wood or concrete and the ceramic tile with mortar attached. This is a thin film crack shield, which will expand or contract especially when installing tile over concrete. While the described method is useful for installing tile over a concrete sub-floor it is not as suitable as the present invention for installing ceramic tile over wood or on wall surfaces in bathrooms and kitchens. A rigid plastic board according to the present invention will provide a firm uncompressible base on a floor of wood or a wall made with wooden or metal studs.
Installing Ceramic Tiles Over Wooden Structure
It is desirable to be able to install a ceramic tile or stone over a wooden or non-concrete slab floor. This is a much more difficult installation, as plywood or other wooden sub-floors are not proper surfaces for the setting of mortar used as a base to accept the stone or ceramic hard surface material. Water and moisture contained in the mortar necessary for the ceramic installation will penetrate the wood sub-floor and cause it to warp resulting in a poor or cracked installation. A specially treated wood is more expensive than the commonly used plywood.
Most multilevel homes in the United States have wooden sub-floors. When ceramic tile is being installed on a concrete floor, weight is not an issue; but is a great concern when installing a ceramic or hard surface floor on a plywood sub-floor. The weight of the stone floor and the materials used in installation must be taken into account. Total weight reduction will be an improvement when installing ceramic and stone flooring over a wood sub-floor.
In residential homes with a basement or crawl space, and in some commercial structures, sub-floors use a layer of plywood as the main flooring surface. The plywood is nailed over supporting floor joists or beams.
Plywood sub-floors flex when walked on. It is therefore necessary to attach a rigid backerboard over plywood in order to install a ceramic tile or stone floor. If a tile floor is installed directly over plywood the tile floor or grout will crack due to the flexing of the wood underneath. A thin plastic film with bubbles, as suggested in U.S. Pat. No. 5,052,161, is adequate over concrete but will not completely solve the problems presented by wood. Moisture from wet mortar necessary to attach the tile will warp the common type plywood used as the sub-floor. A thin film cannot be used as the base for cementing tiles to a wall.
To overcome this problem, skilled workers within the ceramic or stone flooring industry use a "backerboard" that is rigid. The most common rigid backerboard used today are composed of a cementious material encased in a fiberglass or plastic mesh material, which holds it together.
Cementious flooring backerboard is 1/4 to 1/2 inch thick. The board is rigid, therefore once tile is installed over the rigid board; it will not crack due to flexing. A 1/4 or 1/2 inch backerboard is usually the choice for use in the flooring industry. These are heavy usually weighing 40 pounds or 2.67 pounds per square foot. Cementious backerboards are also used in securing ceramic tile to tub surrounds and bathroom or kitchen walls. These backerboards are usually 1/4 to 1/2 inch are heavy and difficult to work with.
The advantage of installing the cementious backerboard over plywood for a hard flooring material underlayment is the fact that it is rigid and that it will readily accept adhesives and mortars. The boards do not flex when walked on and resist moisture making a suitable surface for flooring. When used on walls or countertops the cementious backerboard can be thinner as it is not flexed, but it must be able to withstand wet or moist conditions found in bathrooms and other rooms ordinarily tiled on wall surfaces. The cementious backerboards used on walls, bathtub surrounds and countertops are usually 1/4 thick as they do not have to support a walking person.
When attaching a cementious backerboard to a sub-floor, it is the preferred technique to apply a thin coating of adhesive or mortar to the plywood sub-floor before attaching the backerboard to the top of the plywood floor. The backerboard is usually screwed or nailed to the sub-floor every six inches and placed on joists separated on 16-inch centers to firmly secure the backerboard to the floor. Only enough mortar is applied to level and hold the board but not enough to warp the plywood underneath.
Adhesive or mortar is applied with a notched trowel over the top of the cementious backerboard and the tile is carefully laid out and attached to the adhesive and beat level. This same technique is used to set tiles on backerboards used as bath surrounds on walls and tubs. It is also the method used on countertops that have tile set into them.
Other advantages of using backerboard instead of wood is its ability to withstand moisture, steam, and other types of wetness common to rooms such as kitchens and bathrooms where ceramic tile is usually installed.
While cementious boards are the most common types of backerboards other types of boards such as "Dens-Shield" or "Hardy" backerboard have been introduced to the construction industry. These are slight variations to the backerboard and are made using cement, gypsum, thin plastic laminates and non-woven or fibrous materials. These boards serve the same purpose as the cementious backerboards but are slightly lighter in weight. This makes them easier to work with and more desirable to the craftsman.
U.S. Pat. No. 5,255,482 is a disclosure of a complete flooring structure that consists of a ceramic tile installed over a rigid base, preferably concrete having a crack isolation layer comprised of a plurality of precast sheets made of fired clay, cement or thermosetting resins such as phenolic or two part reactive epoxies or urethane. This disclosure shows the need to overcome expansion and contraction associated with concrete floors. The invention utilizes a sheet containing holes in 20 to 50% of the area available for placing the floor tiles. This approach is useful on concrete but fails to solve the problem of installing ceramic tiles on wooden floors or attaching to studs of a wall.
Another type of backerboard used is plywood specially treated so that it will accept adhesives and mortar designed to set ceramic or stone tile. The plywood is called marine grade and is very expensive. This method is not commonly used because this type of treated plywood is very expensive.
Most cementious backerboards are not structurally sound. Dropping or mishandling a backerboard will result in breakage or crumbling. They must be installed over a plywood sub-floor and are used strictly to provide a rigid surface that will not stress or bend and will readily accept adhesives and mortar used in the hard surface flooring industry. The same boards cannot be used interchangeably for floors and walls.
Cementious backerboards that are common to the industry have many disadvantages that the present invention will overcome. One of the main disadvantages of a cementious backerboard is the fact that it is very heavy. The most used board is 3 ft.times.5 ft 1/2-inch board and weighs 40 pounds or 2.67 pounds per square foot. This added weight must be taken into consideration when assessing whether the floor will support the stone tile or whether it will have to be reinforced. It is also difficult for the skilled craftsman to work with such a heavy board.
Another disadvantage is the fact that cementious backerboards crumble and break very easily. Cementious backerboard are difficult to cut to shapes and sizes other than rectangles and require special tools to accomplish irregular shaped cuts. When the cementious boards are cut with power tools, workers are exposed to dust and other harmful particles. Warnings are commonly placed on these boards to warn the craftsman of the dangers of mishandling.
The heavy weight of the backerboard adds expense for labor and freight. Heavy cementious backerboards that crumble and break require more that one person to carry and transport them when working on a relatively small job. It has been determined by the industry that for a cementious flooring backerboard to provide adequate support, it has to be 1/2 inch thick. The most common size used for flooring backerboard is 3 ft.times.5 ft.times.1/2" when made from a cementious material.
Other boards such, as "Hardybacker" are composed of Portland cement, sand, and cellulose fiber. These boards reduce the problems but still are difficult to work with for the same reason as the cementious boards. They are also brittle and heavy, weighing 30 pounds per 3.times.5 board.
Another product, "Dens-Shield" by Georgia Pacific, is made using gypsum, plastic laminate, and non-woven fibrous laminate. This backerboard is lighter than cementious board but is not as rigid as a cementious board. This board is easily damaged and breaks with normal construction type of handling. Gypsum also absorbs moisture and mortar and is not suitable for most residential flooring construction jobs. When used on floors a flexing occurs which will cause the installed floor to crack.
There is a great need for a rigid backerboard that can be used when installing ceramic tiles on floors, walls, countertops and in other places where mortar or cements should not be directly applied. Ideally the backerboard has to be light in weight, easy to carry and will not be affected by moisture and should be able to withstand flex. In addition, the board should be useful for installing ceramic or stone materials on flooring, walls and countertops. Presently only heavy cementious boards, that are difficult to work with, or expensive specially treated plywood, are available to the construction industry. A great need exists for a backerboard that is rigid, accepts mortar and adhesives, is lightweight and easy to work with.
In addition to the above desirable characteristics, a material that will easily accept flame retardant, anti-microbial chemicals and insect repellents approved by the EPA would be useful in the manufacture of backerboard. The uses for this material would not be limited to the installation of ceramic tile and stone but one skilled in the art could use the boards in other areas such as backerboard for light weight stucco and sheathing in areas where these characteristics are desirable such as non supporting structural trim finish on the outside of buildings.